This invention relates to ultrasonic transducers and, more particularly, to a high temperature ultrasonic transducer.
Ultrasonic flowmeters used to monitor fluids that will propagate sound pulses require a transducer that converts an electrical signal into an ultrasonic acoustical signal. The acoustical signal then is passed through the fluid. In a typical case these acoustical or sound signals are propagated alternately in opposite directions between transducers positioned in upstream-downstream relationship in the fluid flow channel. Because the upstream signal velocity is decreased and the downstream signal velocity is increased by the moving fluid, the alternating pulses yield a frequency or time difference. This time difference is an indication of average flow velocity in the flow channel.
Since the transducers themselves preferably are in intimate contact with the fluid and, in any event, in intimate contact with the pipe containing the fluid, problems are often encountered when the fluid is at a high temperature. At these high temperatures normal materials, epoxy and the like, which are used to position and mount the transducers and to electrically insulate the crystal from its protective housing often becomes softened or destroyed. The faces of a piezoelectric crystal transducer often are painted with a silver or similar electrically conductive paint, and the painted face soldered to an electrical connection by which electrical energy is supplied to the crystal. At high temperatures even these soldered connections tend to soften and become defective.
One transducer is known which is capable of operating under high temperature conditions. This transducer is described in U.S. Pat. No. 3,925,692 issued to Rescheck, et al. Unfortunately, this transducer requires optically flat surfaces to obtain the desired electrical and mechanical couplings. Such requirement renders these transducers relatively expensive to make.
A further problem is encountered in the prior art transducer housings in that unless properly damped, the housings tend to ring and produce unwanted ultrasonic signals in the fluid under test. These undesired signals can cause problems in the accurate measurement of fluid flow.
Accordingly, it is an object of this invention to provide an improved ultrasonic transducer that is capable of operating reliably in relatively high temperatures.